1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a program. More specifically, the present invention relates to an image processing apparatus, an image processing method, and a program that execute a process for generating a motion-compensated image and reducing the noise of an image.
2. Description of the Related Art
An image captured by an imaging device such as a camera or a video camera, for example, includes considerable noise. In particular, an image captured under low illumination or with a short exposure time often includes much noise. This is because the amount of incident light is so small as to reduce the amount of charge stored in an imaging element in the case where an image is captured under low illumination or with a short exposure time. In order to obtain a bright image on the basis of captured data, it is necessary to amplify a signal for the data. While amplifying the signal, noise produced in an imaging element or an analog circuit is also amplified, resulting in an image with much noise.
In order to reduce noise, it is effective to capture an image with a long exposure time. Capturing an image with a long exposure time, however, may cause halation in the image due to hand-shake during exposure. Another approach is to continuously capture images with high shutter speeds that cause substantially no halation due to exposure to obtain an average of the plurality of images captured continuously, reducing noise uncorrelated with time. In this approach, however, the resulting image may be blurred because of camera movement due to hand-shake or a moving subject, or a moving subject may be captured as if captured through multiple exposure, degrading the image.
Examples of techniques for reducing noise in an image according to the related art include:
Japanese Unexamined Patent Application Publication No. Hei 09-261526 (JP-A-Hei 09-261526) discloses a technique to superimpose a plurality of images captured continuously while correcting hand-shake.
Japanese Unexamined Patent Application Publication No. Hei 11-75105 (JP-A-Hei 11-75105) discloses a technique to divide the total exposure time into a plurality of exposure times and add images obtained in the respective exposure times to improve the image quality.
Both the techniques disclosed in JP-A-Hei 09-261526 and JP-A-Hei 11-75105 include detecting a motion vector from a plurality of images to obtain information on motion between the plurality of images and utilizing the motion information to synthesize the images. However, in the case where the images to be processed include subjects with different motions or include a low-contrast image, for example, it may be difficult to detect a motion vector and to correctly correlate the respective motions of the subjects and the motion vector detected from the images. Consequently, the image synthesis process may be performed employing a motion vector with a low precision, degrading the noise reduction effect.